Recording medium, recording apparatus and reproducing apparatus

ABSTRACT

A second generation CD provides improved sound quality over that provided by a first generation CD while remaining compatible with it has a higher sampling rate and has a data format of 1-bit ΔΣ modulation. The higher sampling frequency is an integer multiple of the standard sampling frequency of 44.1 kHz used in the first generation CD to thereby simplify the clock signal generation circuitry. The recording system uses decimation filters to lower the sampling frequency of the 1-bit ΔΣ modulation signal so that the same signal can be used to manufacture both a first generation CD and a second generation CD. The playback apparatus is compatible and the kind of disk is determined based on the table of contents information, so that the appropriate clock signals can be provided to the decoders. In the case of the first generation CD being played back, the data is converted by an oversampling filter and a ΔΣ modulator before being digital to analog converted.

This is a division of application Ser. No. 08/693,440 filed Aug. 7,1996, now U.S. Pat. No. 5,748,594.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a recording medium using anovel data format and to a recording apparatus and a reproducingapparatus corresponding to this recording medium.

2. Description of the Background

Recently, compact disks (CDS) have become highly popularized asrecording media with high sound qualities. A compact disk is adisk-shaped recording medium having a diameter of approximately 12 cm,on which digital audio data is recorded, with a sampling frequency fsselected to be 44.1 kHz and a quantizing bit number selected to be 16bits.

Even more recently, various research has been performed so as to realizesystems with higher sound qualities than those provided by theabove-described CDS, which for the sake of easy explanation will bereferred to as "the first generation CD", in connection with thedevelopment of various media having large storage capacities as well ashigh transfer rates. To realize such higher sound qualities, the firstapproach that was conceived is to increase the sampling frequency.

That is, when a sampling frequency fs is equal to 44.1 kHz as in thefirst generation CD high-frequency components of the audio signal datawould be limited to approximately 20 kHz. On the other hand, by settingthe sampling frequency higher than 44.1 kHz audio data components higherthan 20 kHz can be recorded in order that more naturally sounding audiosignals are recorded/reproduced.

On the other hand, while it is possible to establish a novel CD mediasystem with a data format whose sampling frequency is set to be higherthan that of the first generation CD, there are various practicalproblems in this proposed CD media system.

Principally, even when the above-described CD media system with thenovel format is realized, this novel CD media system should becompatible with the first generation CD in a practical sense.

For instance, a reproducing apparatus corresponding to the novel systemCD with a data format whose sampling frequency is made higher than thatof the first generation CD should also be able to reproduce the firstgeneration CD. In such a case where disk compatibility is added to areproducing apparatus, two separate reproducing-system circuits would atleast be required in the digital section of the system, that is, adecoder and a D/A converter corresponding to the first generation CDwould be required, and another decoder and D/A converter correspondingto the novel system CD would also be required. Moreover, separate clockgenerators would have to be separately employed in the respectivereproducing-system circuits.

This approach would make the circuit arrangement of the reproducingapparatus more complex and larger in scale, as well as raise costs bothof which would be unacceptable.

A playback device with compatibility as described above has inevitablysuch structure as shown in FIG. 6. In FIG. 6, the disk that is mountedon the turntable may be a first generation CD 1a or a second generationCD 1b. When the first generation CD 1a is mounted, a pickup 41 readstable of contents (TOC) information on the inner periphery of the diskwhile the disk 1 is being rotated by a spindle motor 46. A diskdiscriminating unit 42 judges whether the disk 1 is a first generationCD 1a or a second generation CD 1b based on the TOC information.

If the disk 1 is a first generation CD 1a, the disk discriminating unit42 operates switches 51 and 52 to connect the output of each switch tothe respective input terminal T1. An oscillator 43 generates a masterclock signal CK1 having a prescribed frequency for processing the firstgeneration CD 1a, the connection of the output of switch 51 to the inputterminal T1 results in the supply of the master clock signal CK1 to amotor controller 45. The motor controller 45 generates the desiredstandard clock signal by frequency dividing the master clock signal CK1,and using the standard clock signal, the motor controller 45 controlsthe spindle motor 46 so that the disk 1 is rotated at a constant linearvelocity. In this example, the constant linear velocity is thatprescribed for the first generation CD 1a.

The master clock signal CK1 generated by the oscillator 43 is fed to afirst generation CD decoder 47 and a D/A converter 49 for the firstgeneration CD.

The decoder 47 for the first generation CD exercises RF processing,Eight-Fourteen demodulation, and error correction processing to the pitinformation read from the disk 1a by the pickup 41 and outputs digitalaudio data having a sampling frequency fs of 44.1 kHz and a quantizationnumber of 16 bits.

The digital audio data is converted to an analog audio signal by the D/Aconverter 49, and the analog audio signal is output at a terminal 53through the input terminal T1 and the output of the switch 52.

When the second generation CD 1b is mounted, the disk discriminatingunit 42 judges whether the disk 1 is a second generation CD based on theTOC information, and the outputs of switches 51 and 52 are connected tothe respective input terminals T2.

An oscillator 44 generates a master clock signal CK2 having a prescribedfrequency for processing the second generation CD 1b, and the connectionof the output of switch 51 to the input terminal T2 results in thesupply of the master clock signal CK2 to the motor controller 45. Themotor controller 45 generates a desired standard clock by frequencydividing the master clock signal CK2, and using the standard clocksignal the motor controller 45 controls the spindle motor 46 so that thedisk 1 is rotated at a constant linear velocity, which in this exampleis the constant linear velocity prescribed for the second generation CD1b.

The master clock signal CK2 generated by the oscillator is fed to adecoder 48 for the second generation CD and to a D/A converter 50. Thedecoder 48 for the second generation CD exercises RF processing,Eight-Fourteen demodulation, and error correction processing to the pitinformation read from the disk 1 by the pickup 41 and outputs digitalaudio data having a sampling frequency fs of 96 kHz and quantizationnumber of 24 bits.

The digital audio data is converted to an analog audio signal by asecond D/A converter 50, and the analog audio signal is output atterminal 53 through the input terminal T2 and the output of the switch52 as the playback output.

In order to satisfy the compatibility requirement between the firstgeneration CD 1a and the second generation CD 1b, the playback device isinevitably structured as shown in FIG. 6, however, as seen from theabove compatibility requirement such results in complex circuitstructure, large size, and expensive cost of the playback device, thus,this method is considered to be disadvantageous. The requirement of twosets of D/A converters, including peripheral devices of the D/Aconverter such as an amplifier and filter not shown in FIG. 6, is thelargest cause of the complex circuit structure of the playback device.

There is another problem on the CD manufacturing side. For example,considering that both a novel type CD and a first generation CD were tobe manufactured from a certain music source, such as a master tape of amusical composition and the like, the audio signal derived from themaster tape is digitized to produce digital audio data for the noveltype CD, while using, for instance, a sampling frequency of 96 kHz.

As a result, the novel type CD with the high sound quality is realized,but the first generation CD manufactured at the same time with the noveltype CD would have the difficulty that the digital data with a samplingfrequency of 96 kHz must be converted into digital data with a samplingfrequency of 44.1 kHz. At this time, the sound quality of the firstgeneration CD would deteriorate due to the jitter phenomenon caused bythe sampling rate converting process.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention has been made to solve these problems and,therefore, has as an object to provide a novel type recording mediumcapable of having better compatibility with the first generationrecording medium, and also a recording apparatus and a reproducingapparatus that can employ such a novel type recording medium.

More specifically, as a recording medium wherein while a frequency n,where n is an integer, times 44.1 kHz is used as a sampling frequency, adigitized audio signal is recorded thereon. This digitized audio signalis equal to 1 bit ΔΣ-modulated signal.

The present invention provides a recording medium for recording digitalaudio data whose sampling frequency is n, where n is an integer, times44.1 kHz, and also a recording apparatus and a reproducing apparatuscorresponding to this recording medium. Since the sampling frequency ismade higher than 44.1 kHz, a higher sound quality can be realized. Inparticular, since the recording data is ΔΣ-modulated with 1-bitquantization, the sampling frequency can be set to an even higherfrequency, so that higher sound qualities can be sufficiently obtained.

Moreover, since the sampling frequency is an integer multiple of the44.1 kHz employed in the presently available CD system, better matchingcharacteristics between the second generation CD system and thepresently available CD system are obtained. Especially, considering thecompatibility of the recording medium according to the present inventionwith the presently available recording medium, since the samplingfrequency for the recording medium of the present invention is amultiple integer of that for the presently available recording medium,compatibility is realized with the present invention without an overlycomplex circuit arrangement for the reproducing apparatus. Also, as asampling rate converter is not required, there is no deterioration insound qualities caused by jitter components.

Similarly, in the recording apparatus, since it too has good matchingcharacteristics, and since it's sound quality is not deteriorated byjittering, both the recording medium according to the present inventionand the presently available recording medium can be readily manufacturedfor the same sound source.

As a recording apparatus, there are provided digital audio signalproducing means for digitizing an analog audio signal by using asampling frequency n, where n is an integer, times 44.1 kHz to produce adigital audio signal, and recording means capable of performingpreselected recording signal processing on the digital audio signalproduced by the digital audio signal producing means to thereby recordthe processed digital audio signal on a recording medium. Thus, theabove-described new recording medium is capable of being produced.

The recording apparatus is further comprised of a filter means forperforming a decimation process for reducing the sampling frequency by1/n with respect to the digital audio signal produced by the digitalaudio signal producing means, whereby a digital audio signal whosesampling frequency is 44.1 kHz is produced, and a second recording meanscapable of performing predetermined recording signal processing of thedigital audio signal obtained by the filter means to thereby record theprocessed digital audio signal onto a recording medium. As aconsequence, the first generation recording medium whose samplingfrequency is 44.1 kHz may be manufactured without deterioration of thesound quality.

As a reproducing apparatus, there are provided clock generating meansfor generating a clock having a predetermined frequency, decoding meansfor extracting a digital audio signal from information read out from arecording medium based upon a sampling frequency n times 44.1 kHz andemploying the clock output from the clock generating means, and D/Aconverting means for converting the digital audio signal obtained fromthe decoding means into an analog signal. Thus, it is possible torealize a reproducing apparatus corresponding to the above-describedrecording medium.

The reproducing apparatus is further comprised of dividing means fordividing the clock signal generated from the clock generating means intoa second clock signal, and second decoding means for extracting adigital audio signal from the information read out from the recordingmedium based on a sampling frequency of 44.1 kHz with employment of thesecond clock signal. Accordingly, the recording apparatus is madecompatible with the first generation recording medium without a massiveincrease in the scale of the circuit arrangement.

In accordance with another aspect of the present invention, a samplingfrequency conversion means for converting digital data having a firstsampling frequency output from a first decoding means for the firstrecording medium to the digital data having the second samplingfrequency is provided. A D/A conversion means for operating on theoutput generated from a second decoding means for the second recordingmedium and on the output generated from the sampling frequencyconversion means is provided.

More specifically, the D/A conversion means is provided as a conversionmeans for converting digital data having the second sampling frequencyto the analog audio signal, and in respect of the decoded digital datahaving the first sampling frequency, the data having the first samplingfrequency is converted to the data having the second sampling frequency,then, the data having the second sampling frequency is fed to D/Aconversion means to convert the digital data to the analog signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a recording apparatus according to anembodiment of the present invention.

FIGS. 2A-2D are explanatory diagrams for explaining a frequency spectrumof a signal at each operating stage of recording apparatus according tothe embodiment.

FIG. 3 is a block diagram showing a reproducing apparatus according toan embodiment of the present invention.

FIG. 4 is a block diagram showing a reproducing apparatus according toanother embodiment of the present invention.

FIG. 5 is a block diagram showing a reproducing apparatus according toyet another embodiment of the present invention.

FIG. 6 is a block diagram showing a reproducing apparatus that waspreviously proposed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIGS. 1 to 5, embodiments according to the presentinvention will be explained.

As a recording medium in accordance with one embodiment of the presentinvention, a recording medium with a higher sound quality may berealized with respect to the first generation CD whose samplingfrequency fs is equal to 44.1 kHz and whose quantizing bit number isselected to be 16 bits. A sampling frequency of this novel recordingmedium is selected to be 2.8224 MHZ, typically fs is 44.1 kHz and 2.8224MHZ is indicated as 64 fs hereinafter, which is 64 times the samplingfrequency of the first generation CD. Furthermore, a digital audiosignal of this 64 fs sampling frequency, which has been modulated by1-bit ΔΣ modulation, is employed as a digital audio signal to berecorded. Such a recording medium (CD) will be referred to hereinafteras a second generation CD. The above-described second generation CD hasa diameter of approximately 12 cm, the same as that of the firstgeneration CD.

The second generation CD has a diameter of 12 cm, a disk thickness of1.2 mm, and a track pitch of 0.74 μm. The laser wavelength is selectedto be either 650 mm or 635 nm, which is shorter than that for theconventional or first generation, CD. Thus, the recording density of thesecond generation CD is increased to 4.7 Gigabytes to achieve a higherdensity disk.

Furthermore, another second generation CD has been proposed, in whichthe disk thickness of this second generation CD is subdivided into twothicknesses, that is, 0.6 mm and 0.6 mm, so that two recording layersare provided on one surface of the disk. The track pitch is selected tobe 0.74 μm, so that the recording capacity of each recording layer isapproximately 4.7 Gigabytes and, therefore, the entire recordingcapacity of this second generation CD becomes approximately 8.5Gigabytes in total.

In addition to the above-explained disk having the two recording layerson one surface thereof, a still further second generation CD has beenproposed, in which recording regions are formed on both surfaces of thisdisk which has a diameter of 12 cm and a disk thickness of 1.2 mm, andthe track pitch thereof is 0.74 μm. Accordingly, this double recordingsurface disk has a recording capacity of 9.4 Gigabytes in total.

As to the 1-bit ΔΣ-modulated signal, a sampling frequency thereof may beset to achieve considerably higher values of data capacity and datatransfer rate as compared with conventional PCM-modulated signals.Therefore, in accordance with this embodiment of the present invention,while the sampling frequency is selected to be 64 fs, it is possiblethat audio data containing a high frequency component up to 1.4 MHZ maybe recorded/reproduced. As a result, it is possible to provide a secondgeneration CD whose sound qualities are extremely improved compared withthose of the first generation CD.

Also, since the sampling frequency of the second generation CD is aninteger multiple of the sampling frequency of the first generation CD,this second generation CD matches the first generation CD system andcompatibility is maintained.

First, a description will be made of a recording apparatus correspondingto this second generation CD with reference to FIGS. 1 and 2A-2D.

FIG. 1 is a schematic block diagram of a recording apparatus that can beused in the manufacture of the second generation CD, as well as thefirst generation CD.

An analog audio signal is fed in at input terminal 10 as an originalaudio signal derived from a master tape. A frequency spectrum of theanalog audio signal is represented in FIG. 2A.

This analog audio signal is converted into digital data by a 1-bit ΔΣmodulation A/D converter 11. At this time, because the samplingfrequency is selected to be 64 fs a digital audio signal with a 64fs/1-bit format is produced. A frequency spectrum of this 64 fs/1-bitformatted digital audio signal is shown in FIG. 2B. In other words, inprinciple, audio data in a frequency range up to 32 fs may be digitizedand substantially all signal components of the analog audio signal shownin FIG. 2A remain as digital data.

Also, quantizing noise components appear under a condition such thatthey are collected on a high frequency side of a frequency range due tothe noise shaping function achieved in the ΔΣ modulation.

This 64 fs/1-bit digital audio signal is supplied to a recording signalprocessing unit 17 so as to be directly modulated to produce a recordingsignal. That is, the 64 fs/1-bit signal is directly used as the digitalaudio data to be recorded. In the recording signal processing unit 17,for instance, an error correction code is added to the data and also amodulating process such as an Eight-Fourteen Modulation (EFM) forrecording purposes is performed. Then, a signal corresponding to theactual pit information to be formed on a disk is produced as a recordingsignal by this recording signal processing unit 17.

This recording signal is supplied to a disk recorder 18 so as to performa recording operation based on the recording signal, namely, a pitforming operation for an original disk, so that an original CDcomprising music software may be manufactured as the second generationCD 1b. From this original CD 1b manufactured in the above-describedmanner, a stamper (not shown) is fabricated, whereby large numbers ofthe second generation CD 1b may be mass produced using the stamper.

In the case where a first generation CD is also manufactured for thesame music software, the 64 fs/1-bit signal from the ΔΣ-modulation 1-bitA/D converter 11 is supplied to a first decimation filter 12 so as to beconverted into 2 fs (=88.2 kHz)/24-bit digital data. A frequencyspectrum of the 2 fs/24-bit digital data is shown in FIG. 2C. That is,since the sampling frequency is reduced to 2 fs, a data component in afrequency range up to the frequency fs is left.

This 2fs/24-bit digital data is filtered by a second decimation filter13 to become fs(=44.1 kHz)/24-bit digital data. A frequency spectrum ofthe fs/24-bit digital data is shown in FIG. 2D. A data component of afrequency range up to (1/2) fs remains.

The sampling frequency is set to 1/64 by way of these decimation filters12 and 13. This process operation does not correspond to a so-calledsampling rate conversion but, rather, is due to perfectly synchronizeddigital filters for performing the 64:1 decimation. Accordingly, thereis no factor present to cause a jitter component.

This fs/24-bit digital data from the decimation filter 13 is convertedby a bit mapping unit 14 into data whose quantizing bit number is 16bits, which will then be supplied to a recording signal processing unit15. In the recording signal processing unit 15, a preselected processoperation such as adding an error correction code and performingEight-Fourteen Modulation (EFM) is carried out on the fs/16-bit digitalaudio signal so as to thereby produce a recording signal. This recordingsignal is supplied to another disk recorder 16. Based on this recordingsignal, the disk recorder 16 forms pits in an original disk, so that anoriginal CD of the music software is formed as a first generation CD 1a.A stamper (not shown) is fabricated from this original CD 1amanufactured in this manner. Accordingly, the first generation CD 1a isthen mass produced using the stamper.

As described above, in accordance with the recording apparatus of FIG.1, the first generation CD 1a and the second generation CD 1b can bemanufactured. Here, since the 64 fs/1-bit digital audio data is directlyemployed as the recording signal for the second generation CD, thissecond generation CD 1b becomes a disk whose sound quality isconsiderably improved.

Also, since the sampling frequency of the second generation Cd 1b is aninteger multiple of that of the first generation CD, the sound qualityof the fabricated first generation CD 1a is not deteriorated comparedwith that of a conventional first generation CD. In other words, inperforming the sampling frequency conversion only a filtering processfor performing the 1/64 decimation is required and, because the samplingrate converter is no longer required, the jitter components thataccompany sampling rate conversion are not produced. As a consequence,it is possible to achieve a sound quality of this manufactured firstgeneration CD 1a that is equivalent to that of a conventional CDobtained when the analog audio signal is directly sampled by 44.1 kHz.

Next, a description is made of a reproducing apparatus corresponding tothe second generation CD 1b.

FIG. 3 is a schematic block diagram showing major portions of thereproducing apparatus. It should be noted that this reproducingapparatus is also capable of reproducing the first generation CD 1a. Adisk 1, which can be either the first generation CD 1a or the secondgeneration CD 1b, is rotatably driven by a spindle motor 26.

The spindle motor 26 is driven in a constant linear velocity (CLV) modein response to a drive signal from a motor controller 25.

A detailed description of spindle servo operation by the motorcontroller 25 for CLV control is omitted, because such servo systems arewell known. A clock signal CK2 produced by an oscillator 23 is dividedby a divider 24 to thereby obtain a predetermined reference clock signalCKs. Then, a PLL system clock that has been synchronized with thereproduced data is compared in the motor controller 25 with thisreference clock CKs so as to produce an error signal. Power is suppliedto the spindle motor 26 according to this error signal, so that the CLVservo is operated. Although not shown in the drawing, the PLL systemclock may be implemented, for instance, by supplying extracted data intothe PLL circuit within a first generation CD decoder 28 and a secondgeneration CD decoder 29.

While the disk 1 is rotated, a pickup 21 irradiates laser light onto therecording surface of the disk 1, and then the laser light reflected fromthe recording surface thereof is detected by the pickup 21, so that theinformation formed on the disk 1 in the form of pits may be read out.

The information read by the pickup 21 is supplied to a first generationCD decoder 28 and to a second generation CD decoder 29.

A clock signal CK2 having a frequency that will be used to decode thedata in the second generation CD decoder 29 is generated by anoscillator 23, and this clock signal CK2 is supplied to the secondgeneration CD decoder 29. The clock signal CK2 generated by theoscillator 23 is also divided by another divider 27 to produce anotherclock signal CK1 having a frequency that will be used to decode the datain the first generation CD decoder 28, and this second clock signal CK1is supplied to the first generation CD decoder 28.

A 16-bit digital audio signal whose sampling frequency is equal to fs isdecoded and output from the first generation CD decoder 28. This 16-bitsignal is then converted into a 1-bit digital audio signal whosesampling frequency is equal to 64 fs by way of an over sampling filter30 and a ΔΣ modulation circuit 31. Then, this 1-bit digital audio signalis supplied to an input terminal T1 of a switch 32.

The output from the switch 32 is supplied to a 1-bit D/A converter 33 tobe converted into an analog audio signal, which is then output from anoutput terminal 34. To this 1-bit D/A converter 33, the clock signal CK2generated by the oscillator 23, namely, a clock signal identical to theclock signal for the second generation CD decoder 29, is supplied.

A disk discriminating unit 22 functions to discriminate whether theloaded disk 1 is a first generation CD 1a or a second generation CD 1b.This discrimination may be achieved by reading the table of contents(TOC) data recorded on the innermost peripheral side of the disk.

The disk discriminating unit 22 controls operation of the switch 32, aswell as the dividing ratio of the divider 24 according to thediscrimination result.

Operations of the above-described reproducing apparatus will now beexplained.

First, it is assumed that the disk 1 to be reproduced is a secondgeneration CD 1b. When the disk discriminating unit 22 initiallydiscriminates the loaded disk 1 as a second generation CD 1b based uponthe TOC data, the disk discriminating unit 22 sets the dividing ratio ofthe divider 24 to the proper value for a second generation CD 1b. Also,the disk discriminating unit 22 causes the output of the switch 32 to beconnected to a terminal T2.

Since the dividing ratio of the divider 24 is set a the valuecorresponding to the second generation CD 1b, the frequency of thereference clock signal CKs used for the CLV servo in the motorcontroller 25 becomes the frequency corresponding to the secondgeneration CD 1b. That is, the disk 1 is rotatably driven at a linearspeed corresponding to the second generation CD 1b.

At this time, since the pit information extracted by the pickup 21 isdecoded by the second generation CD decoder 29, the 64 fs/1-bit digitalaudio signal is decoded and since the output of the switch 32 isconnected to the terminal T2, the 64 fs/1 bit digital audio signal issupplied to the 1-bit D/A converter 33 so as to be thereby convertedinto the analog audio signal.

Secondly, it is assumed that the disk 1 to be reproduced is a firstgeneration CD 1a, so that when the disk discriminating unit 22 initiallydiscriminates the loaded disk 1 as a first generation CD 1a based uponthe TOC data, the disk discriminating unit 22 sets the dividing ratio ofthe divider 24 to a proper value for a first generation CD 1a. Also, thedisk discriminating unit 22 causes the output of the switch 32 to beconnected to the input terminal T1.

Since the dividing ratio of the divider 24 is set to the valuecorresponding to a first generation CD 1a, the frequency of thereference clock signal CKs used for the CLV servo in the motorcontroller 25 becomes the frequency corresponding to a first generationCD 1a. That is, the disk 1 is rotatably driven at a linear speedcorresponding to a first generation CD 1a.

At this time, since the pit information extracted by the pickup 21 isdecoded by the first generation CD decoder 28, the fs/16-bit digitalaudio signal is properly decoded. This fs/16-bit digital audio signal isprocessed by the over sampling filter 30 and the ΔΣ modulation circuit31, which are operated in response to the clock signal CK2, to beconverted into a 64 fs/1 bit digital audio signal. Then, since theoutput of the switch 32 is connected to the terminal T1, the 64 fs/1 bitdigital audio signal is supplied to the 1 bit D/A converter 33 to bethereby converted into the analog audio signal.

By reproducing the second generation CD 1b in accordance with such areproducing apparatus, audio data with very high sound quality can bereproduced using 64 fs. Also, since the sampling frequency of the secondgeneration CD 1b is an integer multiple of the sampling frequency of thefirst generation CD 1a, as represented in FIG. 3, it is possible torealize a reproducing apparatus having compatibility, even when theclock system and the reproduction system do not involve very complexcircuit arrangements.

In other words, as to the clock system, since the ratio of the samplingfrequency of the first generation CD 1a to that of the second generationCD 1b constitutes an integer ratio, the clock signal from the oscillator23 can be used in common. That is to say, even when a plurality ofoscillators are not employed, it is possible to easily generate clockshaving the necessary frequencies by using frequency dividers. As aresult, two independent master clock systems need not be constructed,and the circuit arrangement of the clock system can be made simple.

Also, with respect to the reproducing system, the 1-bit D/A converter 33can be used in common, so that the circuit arrangement of thereproducing system can also be made simple. Moreover, sound quality doesnot deteriorate using this system.

Since the 1-bit D/A converter 33 is a D/A converter that performsoperations according to data reproduced from the second generation CD1b, there are absolutely no problems with respect to a second generationCD 1b. To also use this 1-bit D/A converter 33 for the data reproducedfrom the first generation CD 1a, fs/16-bit data decoded from the firstgeneration CD decoder 28 must be converted into 64 fs/1-bit data. Sincethe sampling frequency is an integer multiple, however, the fs/16-bitdata is simply oversampled 64 times by the oversampling filter 30 andconverted into 64 fs/1-bit data by the ΔΣ modulation circuit 31. Thus, asampling rate converter is not required. As a consequence, since thereis no factor to produce the jitter component, the sound quality of thefirst generation CD 1a is not deteriorated.

FIG. 4 represents another arrangement of the reproducing apparatus, inwhich the same reference numerals shown in FIG. 3 are employed to denotethe same functional units and explanations thereof are omitted.

In this case, a D/A converter 36 corresponds to a D/A converter operatedin response to the clock signal CK1 and has a sampling frequency fs.

As a result, when the first generation CD 1a is reproduced the fs/16-bitreproduced data output from the first generation CD decoder 28 isdirectly supplied via the switch 32 to the D/A converter 36, so thatthis reproduced data is converted into analog audio data.

On the other hand, when the second generation CD 1b is reproduced, the64 fs/1-bit reproduced data outputted from the second generation CDdecoder 29 is processed in a decimation filter 35 using 64:1 decimationprocessing. Then, since this fs/16-bit reproduced data is supplied viathe switch 32 to the A/D converter 36, this fs/16-bit reproduced data isconverted into analog audio data.

In this case, as with the reproducing apparatus of FIG. 3, compatibilitycan be realized by a simple clock reproducing system, and there is nodeterioration in the sound quality caused by joint use of the D/Aconverter 36. That is, there is no possibility that jitter componentsare produced in the decimation process of the decimation filter 35.

FIG. 5 represents another arrangement of the reproducing apparatus, inwhich the same reference numerals shown in FIGS. 3 and 4 are employed todenote the same functional units and explanations thereof are omitted.

Although the description of the spindle servo operation of the constantlinear velocity control by the motor controller 25 is not repeated, theclock signal CK1 generated by a first oscillator 60 or the clock signalCK2 generated by a second oscillator 61 is fed to the spindle motor 26through the output of a switch 62. The clock signal CK1 or clock signalCK2 is subjected to a required frequency division processing, and thestandard clock signal having a prescribed frequency corresponding to thefirst generation CD 1a or the second generation CD 1b is compared withPLL clock synchronous with the playback data to generate an errorsignal. Then, the control linear velocity servo is exercised by applyingpower to the spindle motor spindle motor depending on the error signal.Although the PL. clock is not shown in the drawings, the PL. clocksignal is generated by feeding the data extracted in the decoder 28 forthe first generation CD when the first generation CD 1a is regeneratedor from the decoder 29 for the second generation CD when the secondgeneration CD 1b is regenerated to the PLL circuit.

When the disk 1 is rotated, the pickup 21 irradiates a laser beam on therecord surface of the disk 1, and the reflected beam is detected to readthe pit information formed on the disk 1.

The information read by the pickup 21 is fed to the decoder 28 for thefirst generation CD and to the decoder 29 for the second generation CD.The decoder 28 for the first generation CD and the decoder 29 for thesecond generation CD each exercise RF processing, Eight-Fourteendemodulation, error correction, and de-interleave processing dependingon the first generation CD 1a and the second generation CD 1b,respectively, to obtain digital audio data.

The clock signal is fed from the oscillator 60 to the decoder 28 for thefirst generation CD as a clock signal for the decoding processing. Theclock signal CK2 is fed from a second oscillator 61 to the decoder 29for the second generation CD as a clock signal for the decodingprocessing. The digital audio signal having a sampling frequency fs of44.1 kHz and a quantization bit number of 16 bit is output from thedecoder 28 for the first generation CD as the decoded output. Thedigital audio signal having a sampling frequency fs of 96 kHz and aquantization bit number of 24 bits is output from the decoder 29 for thesecond generation CD as the decoded output.

The output from the decoder 28 for the first generation CD is fed to asampling rate converter 63. The clock signal CK1 and the clock signalCK2 are fed to the sampling rate converter 63. The sampling rateconverter 63 converts the digital audio signal having a samplingfrequency fs of 44.1 kHz and 16 quantization bits to a digital audiosignal having a sampling frequency fs of 96 kHz and 24 quantizationbits.

The output from the sampling rate converter 63 and the output from thedecoder 29 for the second generation CD are fed to a D/A converter 64selectively by switch 65. The clock signal CK2 is fed to the D/Aconverter 64 as a clock signal for the processing, the D/A converter 64converts the digital audio signal having a sampling frequency fs of 96kHz and 24 quantization bits to the analog audio signal. The analogaudio signal is outputted from the terminal 66 as the playback signal.

The disk discriminating unit 22 is a section for judging whether thedisk 1 mounted is a first generation CD 1a or a second generation CD 1b.The judgment is possible by reading TOC data recorded on the innermostperiphery of the disk. The disk judging section 22 controls the switches62 and 65 depending on the judged result.

Operation of such a playback device is described herein under.

First, operations for playback of the disk 1 of the second generation CD1b are described. The disk discriminating unit 22 judges whether thedisk 1 is a second generation CD 1b based on the TOC data on the disk 1,then, the disk discriminating unit 22 operates the switches 62 and 65 toconnect the outputs thereof to the respective input terminals T2.

Thereby, the clock signal CK2 is fed to the motor controller 25, and thefrequency for the standard clock signal used for the constant linearvelocity servo is converted to the frequency which corresponds to thesecond generation CD 1b. In other words, the disk 1 is drivenrotationally at a linear velocity which corresponds to the secondgeneration CD 1b.

Then, the pit information extracted by the pickup 21 is decoded by thedecoder 29 for the second generation CD, thereby, the digital audiosignal having a sampling frequency fs of 96 kHz and 24 quantization bitsis obtained. When, the switch 65 is connected to the terminal T2,therefore, the digital audio signal of 96 kHz/24-bit format is fed tothe D/A converter 64 and converted to the analog audio signal.

Next, operations for playback when the disk 1 is a first generation CD1a. The disk discriminating unit 22 judges whether the disk 1 is a firstgeneration CD 1a based on the TOC data on the disk 1, then, the diskdiscriminating unit 22 operates the switches 62 and 65 to connect theoutputs thereof to the respective input terminals T1.

Thereby, the clock signal CK1 is fed to the motor controller 25. Thefrequency of the standard clock signal used for the constant linearvelocity servo, which is obtained by frequency dividing the clock signalCK1, is converted to the frequency which corresponds to the firstgeneration CD 1a. In other words, the disk 1 is driven rotationally at alinear velocity which corresponds to the first generation CD 1a.

Then, the pit information extracted by the pickup 21 is decoded by thedecoder 28 for the first generation CD, thereby, the digital audiosignal of 44.1 kHz/16-bit format is decoded.

The digital audio signal of 44.1 kHz/16-bit format is converted to thedigital audio signal of 96 kHz/24-bit format by the sampling rateconverter 29. Then, the output of switch 65 is connected to the inputterminal T1, therefore, the digital audio signal of 96 kHz/24-bit formatis fed to the D/A converter 64 and converted to the analog audio signal.

By using such a playback device, when a second generation CD 1b isregenerated, the audio data of 96 kHz/24-bit format is regenerated toprovide high quality sound.

For playback of the first generation Cd 1a, the decoded digital audiosignal of 44.1 kHz/16-bit format is converted to the digital audiosignal of 96 kHz/24-bit format by the sampling rate converter 63.

Therefore, the D/A converter 64 which corresponds to the digital audiosignal of 96 kHz/24-bit format is used also for playback of the firstgeneration CD 1a, thereby only one set of D/A converting circuits (D/Aconverter, and peripheral devices such as an amplifier and filter) issufficient for the playback circuit, thus, the structure of the playbackcircuit is simplified.

It should be noted that although the above-explained embodiments havebeen described such that the presently available CD system is the firstgeneration CD 1a and the second generation CD 1b has characteristicsthat match those of this first generation CD 1a, the present inventionis not limited to CD systems.

For instance, in a digital tape recorder system it is possible torealize such a recording/reproducing system by employment of a samplingfrequency that is an integer multiple of 44.1 kHz.

Also, in a recording/reproducing system whose sampling frequencies areselected to be 32 kHz and 48 kHz, when the present invention is applied,such a system may be constructed whose sampling frequency is set toeither 32 kHz×n or 48 kHz×n, where n is an integer. In particular, asampling frequency of 48 kHz×n may be suitably used in next-generationvideo recording/reproducing media.

What is claimed is:
 1. A reproducing apparatus for reproducing a firstdigital signal formatted by multi-bit data words sampled at a firstsampling frequency from a first recording medium and a second digitalsignal formatted by 1-bit data words sampled at a second samplingfrequency higher than the first sampling frequency from a secondrecording medium, comprising:a pick-up head for reproducing a digitalsignal from one of the first and second recording medium; first decodingmeans for decoding the multi-bit data words sampled at the firstsampling frequency corresponding to the first recording medium; seconddecoding means for decoding the 1-bit data words sampled at the secondsampling frequency corresponding to the second recording medium;discriminating means for discriminating the first recording medium andthe second recording medium; and switching means for switching digitaloutput signals from the first decoding means and the second decodingmeans in accordance with a result of said discriminating means.
 2. Thereproducing apparatus according to claim 1, further comprising:oversampling means for converting sampling frequency of the digital outputsignal from the first decoding means to the second sampling frequency;delta-sigma modulating means for converting multi-bit data words sampledat the second sampling frequency to 1-bit data words sampled at thesecond sampling frequency.
 3. The reproducing apparatus according toclaim 1, further comprising:down sampling means for converting thesampling frequency of the digital signal from the second decoding meansto the first sampling frequency.
 4. The reproducing apparatus accordingto claim 1, wherein said first decoding means decodes signals from saidfirst recording medium formatted by 16-bit data words sampled at 44.1KHz.
 5. The reproducing apparatus according to claim 1, wherein saidsecond decoding means decodes signals from said second recording mediumformatted by 1-bit data words sampled at 2.8224 MHz.
 6. The reproducingapparatus according to claim 5, wherein a base plate of the secondrecording medium has a diameter not larger than 120 mm and a thicknessof the second recording medium is larger than 0.6 mm.
 7. The reproducingapparatus according to claim 6, wherein a recording track of the secondrecording medium is formed at a track pitch of approximately 0.74 μm andthe track has an information recording capacity of not less than 4.7Gbytes.
 8. The reproducing apparatus according to claim 1, wherein therecording medium is recorded with a high-speed one-bit data streamoutput from a delta-sigma modulation analog to digital converter at asampling frequency of n×44.1 KHz, where n is an integer.
 9. Thereproducing apparatus according to claim 8, wherein a base plate of therecording medium has a diameter not larger than 120 mm and a thicknessof the second recording medium is larger than 0.6 mm.
 10. Thereproducing apparatus according to claim 9, wherein a recording track ofthe second recording medium is formed at a track pitch of approximately0.74 μm and the track has an information recording capacity of not lessthan 4.7 Gbytes.